In the drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluid is common. Hydrocarbons such as oil and gas can be recovered from the subterranean formation using the boreholes. In producing hydrocarbons or the like from loosely or unconsolidated and/or fractured formations, it is not uncommon to produce large volumes of particulate material along with the formation fluids. As is well known in the art, these particulates routinely cause a variety of problems and must be controlled in order for production to be economical. One technique used for controlling the production of particulates (e.g., sand) from a well is one that is commonly known as “gravel-packing.”
In a typical gravel-packed completion, a screen is lowered into the wellbore on a work string and is positioned adjacent to the subterranean formation to be completed, e.g., a production formation. Particulate material, collectively referred to as “gravel,” and a carrier fluid is then pumped as a slurry down the work string where it exits through a “cross-over” into the well annulus formed between the screen and the well casing or open hole, as the case may be. The liquid in the slurry normally flows into the formation and/or through the screen itself, which, in turn, is sized to prevent flow of gravel therethrough. This results in the gravel being deposited or “screened out” in the well annulus where it collects to form a gravel pack around the screen. The gravel, in turn, is sized so that it forms a permeable mass that allows the flow of the produced fluids therethrough and into the screen while blocking the flow of the particulates produced with the production fluids.
One major problem that occurs in gravel-packing single zones, particularly where they are long or inclined, arises from the difficulty in distributing the gravel over the entire completion interval, i.e., completely packing the entire length of the well annulus around the screen. This poor distribution of gravel (i.e., incomplete packing of the interval) is often caused by the carrier fluid in the gravel slurry being lost into the more permeable portions of the formation, which, in turn, causes the gravel to form “sand bridges” in the annulus before all the gravel has been placed.
Such bridges block further flow of slurry through the annulus, which prevents the placement of sufficient gravel below the bridge in top-to-bottom packing operations or above the bridge in bottom-to-top packing operations.
To address this specific problem, “alternate path” well strings have been developed which provide for distribution of gravel throughout the entire completion interval, even if sand bridges form before all the gravel has been placed. In these well screens, the alternate paths are formed by perforated shunts or bypass conduits and extend along the length of the screen and are in fluid communication with the gravel slurry as the slurry enters the well annulus around the screen. Such conduits may be placed on the outside of the screen with another shroud over the alternate paths to prevent them from being damaged during insertion or removal. If a sand bridge forms in the annulus, the slurry is still free to flow through the conduits and out into the annulus through the perforations in the conduits to complete the filling of the annulus above and/or below the sand bridge.
The art would be receptive to alternative and improved alternate path constructions and methods for a gravel packing operation.